Draft copolymer of a mixture of alkyl acrylates on polypropylene and process of preparation



United States Patent Ofifice 3,l62,fi7 Patented Dec. 22, 1964 DRAFT CQPGLYMER F A MHXTURE 0F ALKYL ACRYLATES 0N POLYPRGPYLENE AND PRGC- ES 0F PREPARATION Peter J. Canterino, Clifton, N.J., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Apr. 10, 1961, Ser. No. 101,642 13 Claims. (Cl. 260-878) This invention relates to polypropylene compositions having improved properties. In accordance with one aspect, this invention relates to a process for modifying solid polypropylene to provide a product having improved properties. In accordance with another aspect, this invention relates to a molding composition of improved properties comprising a high surface area form of a modified solid polypropylene.

Polypropylene has been prepared by the use of the so-called organometallic initiator or catalyst systems. These polymers have wide utility in the molding of various articles. Furthermore, polypropylene is particularly useful when a high softening temperature is desired and when considerable pressure is to be applied to the polymeric article, for example, as in plastic pipes.

While polypropylene has many properties which are very desirable, the polymer also has certain properties which make it unsuitable for certain applications. For example, the brittleness temperature, i.e., the temperature at which the material is easily broken, is quite high and the embrittlement time of polypropylene, i.e., the time for air oxidation to cause the polymer to become brittle, is fairly short. While the embrittlement time can be tended, for example, by the incorporation of certain antioxidants and stabilizers, it would be very desirable if the polymer itself could be modified to extend its life without the addition of additives. Also, various materials have been blended with polypropylene to improve its brittleness temperature as well as to improve other properties of the polymer, e.g., its impact strength. For example, certain commercial grades of polypropylene are now being sold which contain polyisobutylene. Although various attempts have been made to improve the properties of polypropylene, there is still room for improvement.

According to the present invention it has been now discovered, quite unexpectedly, that polypropylene having improved properties, especially brittleness temperature, embrittlement time, impact strength, increased dyeability, and the like can be prepared bypolymerizing onto the surface of the solid polymer a mixture of monomers.

Accordingly, an object of this invention is to provide a modified polypropylene having improved properties particularly with respect to brittleness temperature and embrittlement time.

Another object of this invention is to provide an improved method for modifying polypropylene to provide a product having improved properties.

A further object of this invention is to provide a process for forming a molded polypropylene product having improved properties.

Other aspects, objects and the several advantages of the invention are apparent from a study of the disclosure and the appended claims.

According to the invention, solid polypropylene is modified by contacting a high surface area form of the polymer with a mixture of alkyl acryla-te polymerizable monomers and subjecting to polymerization conditions.

More specifically, according to the invention a process is provided for modifying a solid polypropylene which comprises producing such polymer in a form having a high surface area, for example, as finely divided polymer, ap-

polymerization conditions.

plying to said finely divided polymer a monomeric mixture containing at least two polymerizable alkyl acryla-te monomers together with a polymerization catalyst and subjecting the mixture thus obtained to polymerization conditions. The modified polypropylene product thus obtained can then be molded to provide a product having improved properties particularly with respect to brittleness temperature, embrittlement time, impact strength, increased dyeability, and the like.

The alkyl acrylate monomers that can be employed to modify polypropylene according to the invention have the structural formula wherein R is an alkyl radical containing from 1 to 12, inclusive, carbon atoms. Representative examples of alkyl acrylates that can be employed according to the invention include: methyl acrylate, n-propyl acrylate, sec-butyl acrylate, 1,1-dimethylhexyl acrylate, n-decyl acrylate, 3-ethyldecyl acrylate, and the like. The monomeric mixture of acrylates employed preferably will be binary mixtures and will ordinarily contain from 10 to weight percent of one alkyl acrylate, the remainder being another alkyl acrylate.

The polypropylene to be modified according to the practice of the present invention can be prepared by any of the methods which are usually employed in the preparation of these polymers. One suitable known process that can advantageously be employed for the preparation of polypropylene comprises mass polymerization of propylene in the presence of a catalyst or initiator system comprising titanium trichloride, preferably aluminum reduced, and a dialkylaluminum halide, preferably diethylaluminum chloride, and in the presence of a small amount of hydrogen, if desired.

The polypropylene which is contacted with the alkyl acrylate monomeric mixture preferably is in the form of a powder or porous particles or crumb in order that a high surface area is presented on which the monomers are adsorbed or coated. Polypropylene ground by a micropulverizer or similar device, or particles of polypropylene formed in a catalyzed process at a temperature below the solution temperature (particle form polymer), or polypropylene recovered as finely divided particles by any other procedure is suitable for use in the present process. For example, polypropylene particles suitable for use in the invention can be recovered from the effluent of a polypropylene polymerization process by coagulating the polymer as finely divided porous particles by methods well known in the art and then recovering the polymer particles from the resulting dispersion.

As previously indicated, the solid polypropylene is preferably contacted with a mixture of acrylate monomers and a polymerization catalyst and then subjected to Polymerization catalysts that can be used include those of the free radical type such as benzoyl peroxide, dicumyl peroxide, tert-butylbenzene hydro peroxide, potassium persulfate, and the like.

Polymerization conditions of temperature, pressure, etc. normally employed will be ordinarily governed by the monomer-catalyst system employed. The polymerization step will ordinarily be carried out at a temperature between 0 C. and the softening point of the polypropylene, preferably at a tempera-ture below 150 C. The polymerization will generally be carried out for a time in the range between about 0.5 minute and hours.

As indicated above, according to the invention a mixture of polymerizable alkyl acrylate monomers is applied to the polypropylene to be modified together with a polymerization catalyst, subjecting the monomer coated polymer to polymerization conditions, and then recovering a modified polypropylene product having improved properties. A frequently preferred method of operation comprises dissolving from 0.01 to 3.5 weight percent of the catalyst, based on the acrylate monomers, in the monomer mixture prior to its application to the obtained with equivalent amounts of either one of the acrylates alone. As is shown by the specific examples hereinbelow, the modified polypropylenes of this invention have lower brittleness temperatures than untreated polypropylene, longer embrittlernent times than unmodia polypropylene. Alternatively, the catalyst can be apfied polypropylene, and generally higher impact strength. plied to the polypropylene prior to wetting the polymer These improvements in properties are achieved while with the mixture of acrylate monomers. The wetting maintaining a high modulus and the resulting modified step is preferably carried out at a temperature such that polypropylene additionally has increased dyeability. the monomers are in a liquid state. A better understanding of my invention will be ob- Application of the monomer mixture to the polytained on reference to the following illustrative exampropylene can be made by any suitable means. A conples which are not intended, however, to be unduly limivenient method is to tumble the polymer in a drum as tative of the invention. the monomer is added, continuing the tumbling until homogeneous distribution is effected. The amount of EXAMPLE I monomer used will generally be in the range from about A Series of runs was i' out in which P YP PY 1.0 to about 100 weight parts of the monomeric mix- P p in the Presence of an elganomeiaiiie eatet lre per 100 parts of the propylene polymer, preferably lyst system, was treated with various acrylic monomers in the range between about 5 and about 50 parts per 100 in the Presence of a Polymerization catalystparts of polypropylene. The maximum amount will The P p py which Was used in these runs Was depend on the total surface area of the polypropylene P pa y siilriy Poiymerizaiiefl in liquid P py and should not exceed that which can be retained as a in a 3o-ga-iien reaeior- T0 this reader Were ehal'ged 12 coating thereon; that is, there should be no separate grams of titanium triehioride, grams of y monomer phase other than that coating the polypropylene aluminum chloride and 65 Pounds of p y The surface, Operation h ld b d t d under polymerization was carried out for 7.5 hours at 37.8 C. ditions such that the monomer remains in the liquid and 220-230 P- All the end of this time the P yphase, using pressure if necessary. mer was removed from the reactor, washed with a mix- After applying the alkyl acrylate monomer mixture ture of isopropanol and glacial acetic acid at 132 C., and catalyst to the polypropylene, the mixture thus obfiltered and dried- The Weight of the y P y which tained will then be subjected to polymerization condiwas recovered was 9.2 pounds. tions as set forth above. The reaction products obtained Th v -p p p lypr py w h n contacted by the practice of this invention are finely divided, pulwith various acrylic monomers in the presence of a verulent or crumb-like and are free flowing. These prodpolymerilation Catalyst 50 as to eifeet graft p y cts can be molded, drawn or sheeted into films, fibers erization of the acrylic monomer onto the surface of polyor other shaped articles. However, if desired the final P py gross reaction product after polymerization can be treated In a typical run, 200 grams of finely divided polywith a suitable solvent material, for example benzene, propylene was charged to a polyethylene bag and to this to remove acrylate homopolymers formed during polympolymer was applied a solution containing 0.8 gram of erization before subjecting the modified polypropylene benzoyl peroxide in 30 to grams of the acrylic monproduct to molding or other treatment. The final gross 40 omer. The solution of catalyst in monomer was sprayed reaction product ordinarily comprises a graft copolymer onto the polymer. The resulting mixture was then of polypropylene and acrylates, some acrylate homoplaced in a glass jar which was then closed and placed polymer and copolymer, and some polypropylene which in an oven at 70-80 C. overnight. The temperature has not reacted with the acrylate monomers. was then raised to 110 C. for 2 hours to insure com- Although in chemical terminology the term modify plete polymerization. The polymer was then removed when applied to a process involving a polymer may confrom the vessel and milled on a rubber mill to obtain a note an operation in which the molecular structure of homogeneous mixture. Compression molded samples of the polymer is altered, for example, by graft copolymthe material were then formed and physical properties erization, in this specification and claims the term is of these samples were determined. The results of these used in a broader sense. It cannot be said that in the runs are expressed below as Table I. In the following practice of the present invention no graft copolymerizatable the samples which were tested for embrittlement tion occurs. However, the invention is applicable to polytime contain0.2 Weight percent 4,4'-thio-bis(6-tert-butyl mers in which the graft polymerization, by the nature of meta-cresol), which was milled into the polymer on a the polymers used, is relatively small. rubber mill.

Table I Run N0 1 2 3 4 5 6 7 3 9 7 Methyl Butyl Methyl Methyl Methyl Monomer Added None Methyl Acrylate/ Acrylate/ Acrylate/ Butyl Acrylate/ Acrylatc/ Commcrcial Acrylato Styrene Styrene Acrylo- Acrylate Butyl Butyl Polypropylene nitrile Acrylate Acrylate Pts. Monomer/100 Pts. Polymer" 30 12/18 16/24 12/12 32 14/10 15/15 Flcxural Modulus, p.s.i. 8 175,000 127,000 232,000 113,000 238, 000 96,000 122, 000 125,000 170, 000 Hardness, Shore D 4 7e 67 70 74 80 e5 70 69 74 Tensile, Impact, p.s.i. 22. 3 20. 7 15.1 17. 5 16.1 18. 5 19. 5 l 41. 3 I 1. 91 Brittleness Temp, F. 39 57 86 67 70 43 29 13 32 1 Intermediate impact polypropylene, 2 Izod impact strength, by ASTM D-25 5 ASTM D790-49T. 4 ASTM D676-49T sogd under the trade name of Profax A1 and contains polyisobutylene.

B By the method of ASTM D-256 except that test strips are placed on edge.

8 ASTM D746.

The results obtained by polymerization of the mixed acrylate monomers onto polypropylene according to the invention is particularly surprising in that improvements In the above table only Runs 7 and 8, wherein a mixture of methyl acrylate and butyl acrylate were employed, are within the scope of this invention. Runs 2 and 6 in the polymer properties are obtained which cannot be 75 are control runs wherein each of the acrylates was used alone as the monomer. In Runs 7 and 8, it can be seen that the brittleness temperature was greatly reduced, while in the mixtures of acrylates with other monomers (Runs 3-5), the brittleness temperatures were higher than Throughout the application high surface area form is used to denote generically physical forms of the polymer in which the ratio of surface area to volume is high. For example, included are particulate materials, granular when acrylates were used alone (Runs 2 and 6). The 5 powder, and the like, such as described elsewhere in the results obtained in Runs 7 and 8 were unexpected in view application. For the pulverulent material, the polymer of the comparative runs. Further, in Run 8, using a 50/ particles will preferably be 40 mesh or smaller (US. 50 mixture of methyl acrylate and butyl acrylate, a graft Standard Sieve). polymer was obtained having an embrittlement time of As will be evident to those skilled in the art, many 183 hours at 150 C. and 1000 hours at 121 C. compared 10 variations and modifications of the invention can be practo 70 hours and 1000 hours, respectively, for commerticed in view of the foregoing disclosure. Such variacial polypropylene. In determining embrittlement time, tions and modifications are clearly believed to come withstrips 0.5" x 5" x were hung in a circulating air oven in the spirit and scope of the invention. at the indicated temperature and\periodically tested for I claim: embrittlement. Failure was indicated by breaking of the 1. Process for modifying solid polypropylene which is strips when subjected to 180 bend. The tests were disin a form having a high surface area which comprises continued at 1000 hours. polymerizing a mixture of polymerizable monomers there- EXAMPLE H on, and recovering said modified polypropylene, said monomers bemg alkyl acrylates havlng from 1 to 4, in- In another series of runs a mixture of methyl acrylate 20 elusive, carbon atoms in the alkyl groups and being presa d tyl a y Was graft pblymbfilbd 01110 P YP ent in the mixture to the extent of at least 10 weight perpylene and the properties of the resulting polymer were e t of h monomer, compared to blends of polypropylene with the correspond- 2. Process according to claim 1 wherein said monomer ing amounts of methyl acrylate-butyl acrylate copolymer. mixture comprises methyl acrylate and butyl acrylate.

The polypropylene Which Was us d in these runs W218 3. Process according to claim 2 wherein said mixture prepared by the procedure described in Example I except comprises approximately a 50-50 mixture of said acrylates. that a S-gallon reactor was employed and hydrogen was 4. A process for modifying a solid polypropylene to present in the polymerization zone. One gram of TiCl improve its brittleness temperature which comprises proand 2.32 grams of diethylaluminum chloride (in heptane ducing said polymer in a form having a high surface area, solution) were charged 10 the reactor and maintained in applying to said polymer 9, monomeric mixture containcontact with liquid propylene at 37.8 C. for 3 hours in ing at least 10 weight percent of each of two polymerizable the Presencb Of 9960 0f bydl'bgbn a d at alkyl acrylate monomers having from 1 to 4, inclusive, mospheric conditions). The yield of polymer was 439 carbon atoms in the alkyl groups together with a polymgrams and this polymer was Washed with methanol in a erization catalyst, subjecting the mixture to polymeriza- Waring Blendor and dried. V 5 tion conditions, and recovering said modified polypro- In Run 10, 100 parts of the polypropylene was blended pylene. with 36 parts of poly(methy1 acrylate) which had been 5. Process according to claim 4 wherein said monomer p p y s on polymerization. The blending was mixture comprises methyl acrylate and butyl acrylate. Car 011 a rubber mill, but geneous blend of 6. Process according to claim 5 wherein said mixture is th materials Could not be obtained- In Run 11, 100 40 approximately a 50-50 mixture of said acrylates and the parts of the polypropylene was blended with 36 parts of amount of said mixture applied ranges from about 5 to a 50/50 methyl acrylate/butyl acrylate copolymer which b t 50 i h parts per 100 i h parts f 1 had been prepared by emulsion polymerization. This 1 blending was carrled out on a rubber null and in this case 7. A process f forming a molded product which 001m a hOmoggnewsblend was Obtamedprises inserting into a molding zone a moldable composi- In the mventlon run (R119 5% 100 parts the l tion comprising a high surface area form of polypropyl- Propylem was contacted Wlth parts. of a /50 one having a coating formed by polymerizing a mixture ture of methyl acryl'ate/butyl acr-ylate 1n the presence of f alk 1 1 t h fr 1 t 4 I 0.8 part benzoyl peroxide under the conditions set forth 0 y any monomers avmg 0m 0 mo uslve in Example I. This graft polymer was milled on a rubber 5 carbon "f the alkyl groups on the surface thereof, mm to obtain a homogeneous mixture" and sub ecting to molding conditions, said monomers In each of the runs 02 Weight percent of the antioxi being present in the mixture to the extent of at least 10 dant employed in Example I was milled into the polymer Welght Percent of each manometon the rubber mill. The properties of the polymers A molding Composition Comprising a high Surface which were prepared in these runs are expressed below as area form of P YP PY having a Coating formed by Table II. polymerizing on the surface of said polymer a mixture Table H Run No 10 11 12 Propylene 50/50 Methyl Polypropylene Blended With Acrylate/Butyl Aerylate Graft Polymer Blended With 50/50 Methyl It can be seen that the graft polymer has a lower brittleness temperature, a higher impact strength and a higher melt index than the control runs which were formulated by blending.

of alkyl acrylates having 1 to 4, inclusive, carbon atoms in the alkyl groups, said monomers being present in the mixture to the extent of at least 10 weight percent of each monomer.

9. Composition according to claim 8 wherein said mixture comprises methyl acrylate and butyl acrylate.

l0. Composition according to claim 9 wherein said mixture is approximately a 50-50 mixture of methyl acrylate and butyl acrylate.

11. Process according to claim 2 wherein said mixture comprises approximately a 60 methyl acrylate/40, butyl acrylate mixture.

12. Process according to claim 5 wherein said mixture is approximately 60 methyl acrylate/40 butyl acrylate and the amount of said mixture applied ranges from about 5 to about 50 weight parts per 100 weight parts of polypropylene.

13. Composition according to claim 9 wherein said mixture is approximately 60 methyl acrylate/40 butyl acrylate.

References Cited in the file of this patent UNITED STATES PATENTS 2,837,496 Vandenberg June 3, 1958 2,987,501 Rieke et a1. June 6, 19,61

FOREIGN PATENTS 814,393 Great Britain June 3, 1959 553,779 Belgium June 28, 1957 

1. PROCESS FOR MODIFYING SOLID POLYPROPYLENE WHICH IS IN A FORM HAVING A HIGH SURFACE AREA WHICH COMPRISES POLYMERIZING A MIXTURE OF POLYMERIZABLE MONOMERS THEREON, AND RECOVERING SAID MODIFIED POLYPROPYLENE, SAID MONOMERS BEING ALKYL ACRYLATES HAVING FROM 1 TO 4, INCLUSIVE, CARBON ATOMS IN THE ALKYL GROUPS AND BEING PRESENT IN THE MIXTURE TO THE EXTENT OF AT LEAST 10 WEIGHT PERCENT OF EACH MONOMER. 